Gas Lift Valve for High Pressure Operation

ABSTRACT

A unique gas lift valve bellows assembly in which an internal piston incorporated within the bellows provides over travel prevention and over pressure protection during valve operation, independent of the set or operating gas pressures exerted on the gas lift valve. The piston separates a hydraulic damping reservoir in the interior convolutions of the bellows from the upper gas volume chamber. The piston travels a pre-set distance between two stops to provide a fluid dampened hydraulic balance across the bellows convolutions in both the open and closed positions of the valve. This results in a long lived bellows valve that can operate with any pressure up to the limits of the material, without overstressing the bellows.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to gas lift valves for the artificialproduction from oil and gas wells and, more particularly, to gas liftvalves capable of operating at high differential pressures.

2. Description of Related Art

Gas lift valves have been used for many years to inject compressed gasinto oil and gas wells to assist in the production of well fluids to thesurface. The valves have evolved into devices in which a metal bellows,of a variety of sizes, converts pressure into movement. This allows theinjected compressed gas to act upon the bellows to open the valve, andpass through a control mechanism into the fluid fed in from the well'sproducing zone into the well bore. As differential pressure is reducedon the bellows, the valve can close. Two types of gas lift valves usebellows. The first uses a non-gas charged, atmospheric bellows andrequires a spring to close the valve mechanism. The other mechanism usesan internal gas charge, usually nitrogen, in the bellows and volume dometo provide the closing force for the valve. In both valveconfigurations, pressure differential on the bellows from the injectedhigh pressure gas opens the valve mechanism.

In the case of the non-gas charged bellows, the atmospheric pressurizedbellows is subjected to high differential pressures when the valve isinstalled in a well and exposed to high operating gas injectionpressure. The nitrogen charged bellows is subject to high internalbellows pressure during setting and prior to installation. Onceinstalled, the differential pressure across the bellows is less than ina non-gas charged bellows during operation of the valve. Highdifferential pressure across a bellows during operation reduces thecycle life of the bellows. The existing gas lift valves and bellows arenot designed to operate with set pressures or in operating pressures inexcess of 2000 psig without severe failure risks. Some existing valvebellows do have some fluid and/or mechanical protection for overpressuredue to operating pressures in the fill open position. However, noneprovide for protection from differential overpressure from the setpressure in the bellows.

SUMMARY OF THE INVENTION

The present invention comprises a gas-charged gas lift valve wherein thebellows of the gas lift valve are protected from high differentialpressure. A piston is disposed in a central bore of a sleeve in thebellows. The piston separates a hydraulic damping reservoir in theinterior convolutions of the bellows from the upper gas volume chambercontaining the gas charge. The piston can only travel a pre-set distancein the internal bore between two stops. When operating pressure exertedon the bellows from the injected gas exceed the pressure of the gascharge in the upper gas chamber, the piston is pushed to contact theupper stop. More of the hydraulic dampening fluid is allowed to exit theinterior of the bellow convolutions and move into the central bore ofthe internal sleeve. This allows the pressure from the injected gas tomove the bellows into a contracted position to open the valve. Once thepiston has reached the top position, the incompressible nature of thehydraulic fluid protects the bellows from any further increase inexternal pressure as well as further contraction due to that pressure.When the operating pressure of the injected gas drops below the pressureof the upper gas chamber, the gas in the upper gas chamber pushes thepiston to the lower stop. This forces more of the hydraulic dampeningfluid in the interior of the bellow convolutions, extending the bellowsand closing the valve. Once the piston reaches the bottom position, theincompressible nature of the hydraulic fluid prevents the bellows fromfurther extension and prevents a large pressure differential across thebellows.

The bellows design in the disclosed invention provides a fluid dampenedhydraulic balance across the bellows convolutions in both the open andclosed positions of the valve. It also preferably eliminates pressuredifferentials in excess of the natural spring rate of the bellowsmaterials and any small compression resistance of the nitrogen chargedgas in the dome/bellows volume. Since this new device prevents highdifferential pressure across the convolutions of the bellows, the valvecan preferably be charged with any pressure up to the limits of thematerials and can be run in any operating pressure up to the limits ofthe materials, without overstressing the bellows. This can provide along lived bellows operation, approaching the life cycle ratings of thebellows manufacturer under low stressed conditions. The new bellowsdevice can also preferably be retrofitted into existing gas lift valveconfigurations.

BRIEF DESCRIPTION OF THE DRAWINGS

The apparatus of the invention is further described and explained inrelation to the following figures wherein:

FIG. 1 is a cross-sectional view of a typical wire line retrievable highpressure gas lift valve of the preferred embodiment;

FIG. 2 is a cross sectional view of the upper chamber of the preferredembodiment illustrated in the fully extended position with the pistonlocated at the lower travel stop;

FIG. 3 is a cross sectional view of the upper chamber of the preferredembodiments from FIG. 1, illustrated in the fully contracted conditionwith the piston located at the upper travel stop.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Various aspects and relationships of a preferred embodiment of thecurrent invention will be described in the context of what is commonlyknown to the industry as a casing sensitive one inch wire lineretrievable gas lift valve. It is within the scope of this patent toapply the present invention to other sizes and configurations of gaslift valves, both wire line retrievable and tubing retrievable gas liftvalves and both injection pressure operated (IPO) or production pressureoperated (PPO) valves.

FIG. 1 illustrates a gas lift valve 11 into which the present inventionhas been adapted. The valve 11 consists first of an upper chamber 1,which includes a tail plug 2, a sealing gasket 3, a core valve 4, and aset of external seals 34 employed to pack off the valve in the upperseal bore of an appropriate side pocket gas lift mandrel common to theindustry and not illustrated herein. The upper chamber 1 is attached bymeans of a threaded connector or other suitable means to the improvedmetal bellows assembly 5 of the present invention, and is enclosed by aported bellows housing 23.

The improved metal bellows assembly 5 of the present invention consistsof a metal bellows 6, an upper bellows adaptor 7, a lower bellowsadaptor 8, an internal ported sleeve 9, a piston 10, an adjustment screw19, and a stem adaptor 12, to which is attached a stem 35. The metalbellows 6 is attached to the upper bellows adaptor 7 and the lowerbellows adaptor 8 by any of the means of soldering, brazing, or weldingto produce a strong hermetic seal between the metal bellows 6 and theupper and lower bellows adaptors 7, 8. The improved metal bellowsassembly 5 is sealed to the upper chamber 1 by the use of O-rings 36 orany other suitable means.

The internal ported sleeve 9 has a small fluid port 13 through whichhydraulic fluid is able to communicate from the annulus 15 created bythe internal ported sleeve 9 and the interior of the metal bellows 6 tothe internal seal bore 16 of the internal ported sleeve 9, and to actupon the piston 10. The piston 10 having external resilient seals 17 islocated in the internal seal bore 16 of the internal ported sleeve 9 andis allowed to travel between the upper travel stop 18 and the lowertravel stop 19. Lower travel stop 19 can optionally be an adjustmentscrew. The use of an adjustment screw as travel stop 19 allows the rangeof movement of piston 10 to be limited and thus the amount of extensionof bellows 6. The internal ported sleeve 9 also has external seals 20 toseal it to the internal seal bore 21 of the upper bellows adaptor 7, anupper travel stop shoulder 22, and is allowed to travel within the upperadaptor 7 within travel limits imposed by the upper travel stop shoulder22 and the piston's lower travel stop 19.

Upper chamber 1 contains compressed gas, typically nitrogen, in chamber37 that exerts a downward force upon the piston 10. This pushes thepiston 10 downward forcing the incompressible hydraulic fluid located inthe internal seal bore 16 below the piston 10 in an external directionthrough the small fluid port 13 and into the annulus 15 created by theinternal ported sleeve 9 and the interior surface of the metal bellows6. Increased hydraulic fluid in annulus 15 causes the metal bellows 6 toextend. FIG. 2 will illustrate this condition. Compressed gas 38 fromthe casing-tubing annulus (not illustrated) injected from the surfacewellhead provides a counteracting force on the external surface of themetal bellows 6. When the force of compressed gas 38 is larger than thedownward force upon the piston 10 of the compressed gas located inchamber 37, the metal bellows 6 contract. FIG. 3 will illustrate thiscondition.

The gas lift valve 11 of the preferred embodiment further comprises astem adapter 12 secured to the lower bellows adapter 8. Stem 35 issecured in stem adapter 12 and is positioned proximate to seat 32. Uponextension of bellows 6, lower bellows adapter 8, and thus stem adapter12, and stem 35 are translated toward seat 32. When bellows 6 are fullyextended, stem 35 is seated in seat 32, thereby preventing injection gas38 from passing through opening 40. This represents the ‘closed’position of valve 11. Upon contraction of bellows 6, lower bellowsadapter and thus stem adapter 12 and stem 35 are translated away fromseat 32. This allows injection gas 38 to pass through opening 40 and outthrough nose cap 25 of valve 11. This represents the ‘open’ position ofvalve 11.

As shown in FIG. 1, the gas lift valve 11 of the preferred embodimentfurther consists of a check valve assembly 24 common to the industry.Check valve assembly 24 comprises a nose cap 25, and back check dart 26,a spring 27, a resilient seal 28, a seal support washer 29, and a backcheck adaptor 30. The valve further consists of a lower packing adaptor31, in which is also located a seat 32 and a retaining ring 33 tocapture the seat in the lower packing adaptor, and on which is located aset of external seals 34 employed to pack off the valve in the lowerseal bore of an appropriate side pocket gas lift mandrel common to theindustry and not illustrated herein.

FIG. 2 illustrates the upper chamber 1 and improved metal bellowsassembly 5 of the present invention with the bellows 6 in the fullyextended condition and the internal piston 10 located against the lowertravel stop 19. Optionally, the lower travel stop 19 may be anadjustable screw to provide additional control over the distance thatthe piston 10 can move in internal sleeve 9. The fully extendedcondition of the improved metal bellows assembly 5 is obtained when thepressure exerted upon the internal surfaces of the metal bellows 6exceeds the pressure exerted upon the external surfaces of the metalbellows 6.

The pressure of the compressed gas in the chamber 37 acts upon the areaof the external seals 20 on the internal sleeve 9 and the externalresilient seals 17 on the piston 10 to provide a downward force thattends to extend the metal bellows 6 and move the piston 10 downward. Asthe piston 10 travels downward in the internal seal bore 16 of theinternal ported sleeve 9, it forces the hydraulic fluid in the internalseal bore 16 through the small fluid port 13 and into the annulus 15created by the exterior of the internal ported sleeve 9 and the interiorsurface of the metal bellows 6. The pressure transferred to the internalsurface of the metal bellows 6 by the displaced hydraulic fluid 14causes the metal bellows 6 to extend. When the piston 10 travels to andis stopped by the lower travel stop 19 in this embodiment, no furtherhydraulic fluid 14 may be displaced into the annulus 15 created by theinternal ported sleeve 9 and the interior surface of the metal bellows6, thereby protecting the metal bellows 6 from any further increase ininternal pressure, and thus also from any further extension or increasedinternal forces which would otherwise overstress the metal bellows 6.

When the improved metal bellows assembly 5 is in the fully extendedposition, less a small predetermined distance, and the piston 10 iswithin the same small predetermined distance from the lower travel stop19, stem 35 first contacts and seals to the seat 32, thereby preventinginjected gas 38 from passing through the valve 11. The inherentdiametric flexibility of the metal bellows allows the piston 10 tocontinue until it contacts the lower travel stop 19. Once the piston 10contacts the lower travel stop 19 any further extension of the metalbellows 6 is restricted due to the incompressibility of the containedhydraulic fluid in annulus 15.

FIG. 3 illustrates the preferred embodiment of the present invention inthe fully contracted condition, with the upper travel stop shoulder 22of the internal ported sleeve 9 against the upper bellows adaptor 7 andthe internal piston 10 located against the upper travel stop 18. Thefully contracted condition of the improved metal bellows assembly 5 isobtained when the pressure of injected gas 38 exerted upon the externalsurfaces of the metal bellows 6 exceeds the pressure exerted upon theinternal surfaces of the metal bellows 6 from the compressed gas inchamber 36. This would occur when the pressure of the injected gas 36 israised above a certain threshold.

When the pressure of the injected gas 38 is above the threshold, itforces the metal bellows 6 to contract, thus displacing the hydraulicfluid 14 from the annulus 15 created by the exterior of the internalported sleeve 9 and the interior surface of the metal bellows 6 and intothe internal seal bore 16 of the internal ported sleeve 9. The increasedamount of hydraulic fluid 14 in the internal seal bore 16 forces thepiston 10 in an upward direction, until it reaches the upward travelstop 18. The contraction of the metal bellows also moves internal sleeve9 upward until a shoulder 22 on internal sleeve contacts upper bellowsadapter 7. This raises stem 35 off of seat 32, thereby allowing injectedgas 38 to pass through the valve. Upon reaching the upward travel stop18, the piston 10 creates an impassable barrier for the hydraulic fluidin internal seal bore 16. The incompressible hydraulic fluid remainingin annulus 15 thereby protects the bellows from any further increase inexternal pressure, and thus also from any further contraction orincreased external forces which would otherwise overstress the metalbellows 6.

The above descriptions of certain embodiments are made for the purposesof illustration only and are not intended to be limiting in any manner.Other alterations and modifications of the preferred embodiment willbecome apparent to those of ordinary skill in the art upon reading thisdisclosure, and it is intended that the scope of the invention disclosedherein be limited only by the broadest interpretation of the appendedclaims to which the inventor is legally entitled.

1. A gas lift valve capable of withstanding high differential pressurecomprising: bellows containing a plurality of convolutions, wherein thebellows can contract and expand; an upper adapter secured to a first endof the bellows and containing a charge of gas; a lower adapter connectedto a second end of the bellows; a sleeve disposed within the bellows, afirst end of the sleeve secured to the lower adapter, and a second endslidably disposed through the upper adapter; a central bore in thesleeve, wherein a first end of the central bore is in fluidcommunication with the charge of gas in the upper adapter; a piston withan external seal slidably disposed in the internal bore of the sleeve; afirst and second travel stop limiting the movement of the piston withinthe bore, wherein the first travel stop is located toward the first endof the central bore and the second travel stop is located toward thesecond end of the central bore; a longitudinal fluid port at the secondend of the sleeve providing fluid communication between the inside ofthe convolutions of the bellows and the internal bore of the sleeve; anincompressible fluid located inside the convolutions of the bellows;wherein upon contraction of the bellows, the piston travels to the firsttravel stop, allowing more of the incompressible fluid to move from theinterior of the bellows convolutions to the central bore through thefluid port; wherein upon extension of the bellows, the piston travels tothe second travel stop, forcing more of the incompressible fluid fromthe central bore into the interior convolutions of the bellows; a fluidselected from the group consisting of an injection gas and a well fluid,wherein the fluid is located exterior of the bellows and provides anexternal pressure on the bellows; wherein the amount of incompressiblefluid in the interior bellows convolutions when the piston is at thefirst and second travel stops is sufficient to provide an internalpressure that is approximately the same as the exterior pressure on thebellows from the injection gas.
 2. The gas lift valve of claim 1 whereinthe valve is opened when the external pressure is greater than thepressure of the internal charge of gas and the valve is closed when theexternal pressure is less than the pressure of the internal charge ofgas.
 3. The gas lift valve of claim 2 further comprising a shoulder onthe sleeve, wherein the shoulder limits the contraction of the bellowsby contacting the upper adapter;
 4. The gas lift valve of claim 2further comprising a valve stem secured to the lower adapter, a valveseat disposed adjacent to the valve stem, wherein upon extension of thebellows, the valve stem seats in the valve seat, closing the valve andupon contraction of the bellows, the valve stem disengages from thevalve seat, opening the valve.
 5. The gas lift valve of claim 1 whereinthe gas lift valve is a tubing retrievable valve.
 6. The gas lift valveof claim 1 wherein the gas lift valve is a wire line retrievable valve.7. The gas lift valve of claim 1 wherein the lower travel stop is anadjustable screw, wherein the adjustable screw can be adjusted to limitthe travel of the piston.
 8. The gas lift valve of claim 1 wherein theupper adapter further comprises, a chamber which contains the charge ofgas, a core valve, and an external seal to seal the valve in an upperbore of a side pocket gas lift mandrel.
 9. The gas lift valve of claim 1wherein the bellows are metal.
 10. The gas lift valve of claim 1 furthercomprising a lower packing adapter comprising an external seal to sealthe valve in a lower bore of a side pocket gas lift mandrel and theseat.
 11. The gas lift valve of claim 10 further comprising a checkvalve assembly secured to the lower packing adapter.
 12. A gas liftvalve capable of withstanding high differential pressure comprising:bellows containing a plurality of convolutions, wherein the bellows cancontract and expand; an incompressible fluid located in the interior ofthe bellows convolutions providing an interior pressure; a reservoir influid communication with the interior of the bellows convolutions; afluid selected from the group consisting of an injection gas and a wellfluid, wherein the fluid is exterior to the bellows and provides anexterior pressure; piston means located within the bellows for moving aportion of the incompressible fluid between the interior of the bellowsconvolutions and the reservoir to maintain the interior pressure that isapproximately the same as the exterior pressure.
 13. The gas lift valveof claim 12 wherein the reservoir is a portion of a central bore in asleeve located within the bellows and a longitudinal port provides fluidcommunication between the reservoir and the interior of the bellowsconvolutions.
 14. The gas lift valve of claim 13 wherein the pistonmeans is a piston with an external seal slidably disposed within thecentral bore of the sleeve between a first and second travel stopwherein the second travel stop is located proximate to the longitudinalport.
 15. The gas lift valve of claim 14 further comprising an internalcharge of gas in fluid communication with the central bore opposite fromthe longitudinal port.
 16. The gas lift valve of claim 15 wherein thebellows contract to open the valve when the external pressure is greaterthan the pressure of the internal charge of gas and the bellows extendto close the valve when the external pressure is less than the pressureof the internal charge of gas.
 17. The gas lift valve of claim 16further comprising an upper adapter secured to a first end of thebellows and a shoulder on the sleeve, wherein the shoulder limits thecontraction of the bellows by contacting the upper adapter.
 18. The gaslift valve of claim 16 further comprising a valve stem secured to thelower adapter and a valve seat disposed adjacent to the valve stem,wherein upon extension of the bellows, the valve stem seats in the valveseat, closing the valve and upon contraction of the bellows, the valvestem disengages from the valve seat, opening the valve.
 19. The gas liftvalve of claim 18 wherein the contact of the valve stem to the valveseat limits the extension of the bellows.
 20. The gas lift valve ofclaim 14 wherein upon contraction of the bellows, the piston travels tothe first travel stop, allowing more of the incompressible fluid to movefrom the interior of the bellows convolutions to the central borethrough the fluid port and upon extension of the bellows, the pistontravels to the second travel stop, forcing more of the incompressiblefluid from the central bore into the interior convolutions of thebellows.
 21. The gas lift valve of claim 12 wherein the lower travelstop is an adjustable screw, wherein the adjustable screw can beadjusted to limit the travel of the piston.
 22. The gas lift valve ofclaim 12 further comprising external seals to seal the valve in a boreof a side pocket gas lift mandrel.
 23. The gas lift valve of claim 18further comprising: an upper adapter secured to a first end of thebellows and a shoulder on the sleeve, wherein the shoulder limits thecontraction of the bellows by contacting the upper adapter; externalseals to seal the valve in a bore of a side pocket gas lift mandrel;wherein upon contraction of the bellows, the piston travels to the firsttravel stop, allowing more of the incompressible fluid to move from theinterior of the bellows convolutions to the central bore through thefluid port and upon extension of the bellows, the piston travels to thesecond travel stop, forcing more of the incompressible fluid from thecentral bore into the interior convolutions of the bellows.